Hydraulic pressure transmitting fluid



Patented May 3, 1949 HYDRAULIC PRESSURE TRANSMITTING FLUID Chester M. White, Rochester, N. Y., assignor to Genesee Research Corporation, Rochester, N. Y., a corporation of New York No Drawing. Application March 18, 1947, Serial No. 735,527

Claims. (Cl. 25278) The present invention relates to a new and improved hydraulic pressure transmitting fluid which, while not limited thereto, is particularly adapted for use as a hydraulic medium in hydraulic brake systems, hydraulic shock absorbers, hydraulic presses, and other fluid pressure actuated mechanism.

In spite of extended research in an effort to develop substitutes, castor oil is today the most commonly employed base or lubricant in hydraulic pressure transmitting fluids. Possibly the greatest drawback and disadvantage attending the use of castor oil for this purpose is its tendency to oxidize and form athick and tacky film on the moving parts of the hydraulic pressure system in which it is employed. An almost equally serious disadvantage of castor oil base fluids is their comparatively low water tolerance. Straight castor oil fluids may be separated into phases due to the presence of water of condensation.

The foregoing and other disadvantages of castor oil are obviated by the present invention and while, inone sense, the invention may be said to encompass hydraulic pressure transmitting fluids in which a new material is substituted for castor oil, it is not to be construed in such a narrow sense. The compositions of the invention are preferably free from castor oil but, when necessary, they may be readily mixed with commercial castor oil or other base fluids in com-- men use in hydraulic systems today.

According to the invention, the improved hydraulic fluids contain tricresyl phosphate as their lubricating base. By lubricating base is meant that the tricresyl phosphate comprises a substantial proportion and at least ten per cent of the hydraulic pressure transmitting fluid. It has been found that tricresyl phosphate is stable under heat and will not polymerize or gum up under hydraulic pressure use. Furthermore, it will not break down into its components, phosphoric acid and cresol, and it therefore does not exhibit corrosive tendencies to metals in the hydraulic pressure system. The discovery that tricresyl phosphate could be used as the lubricating base in hydraulic pressure transmitting fluids is indeed surprising for this reason. The decomposition of esters is one of the reasons that this class of compounds is generally not employed in brake fluid formulations. As stated above, tricresyl phosphate does not break down under conditions of use. Furthermore, it is quite surprising that this compound does not swell rubber excessively, since it is an aromatic compound, and aromatic compounds are noted for their capacity to cause rubber swelling.

Broadly stated, the hydraulic pressure transmission fluids of the present invention contain tricresylphosphate as their lubricating base,

along with solvents or diluents, and, if necessary or desirable, very small amounts of corros1on 1nhibitors, such as amine phosphates and nitrites.

As diluents 'or solvents, there may be employed, either singly or in combination one with the other,

a polymerized glycol and/or an aliphatic ether,

of a polyglycol. As used herein, the term polymerized glycol may include the specific compounds diethylene glycol, and triethylene glycol, as well as polymerized ethylene glycols having molecular weights up to 250, and the specific compounds dipropylene glycol and tripropylene glycol as well as polymerized propylene glycol. For the polymerized glycol content, there may be substituted, to the extent of not more than fifty per cent, so-called higher glycols such as butylene glycol, amylene glycol and hexylene glycol.

The alcohol ethers maybe methyl, ethyl, propyl, butyl, etc. ethers of ethylene glycol, di-

.' ethylene glycol, triethylene glycoLtetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol and tetrapropylene glycol. Preferably, mixtures of the foregoing alcohol ethers are employed.

The following general'formulation having the range of ingredient proportions indicated embraces a number of highly desirable fluids for.

use in hydraulic brake systems:

Per cent by weight Tricresyl phosphate (Tech.) 10-50 Polymerized glycol (single or mixed) 0-85 Aliphatic ethers of polyglycols (single or mixed) '0-85 Per cent by weight Tricresyl phosphate (Tech.) 20.00 Dipropylene glycol 40.00 Ethyl ether or triethylene glycol 39.10 Diamylamine phosphate 0.05

Diisopropylamine nitrite 0.05

3 In order to illustrate the desirability of the foregoing specific brake fluid formulation, its critical physical data is given below:

Boiling point 157 C.

Viscosity 100 F 13 1 Viscosity -40 F. 19,566 018.

Rubber swelling 0.030" (heated 5 days Cold test Clear; .flows after 11 Water tolerance water-clear and flowsafterdl days-@ -50'!.

Miscibility Castor oil base fluids" clear and -flow after 11 days 50 F. Corrosion (7 days 200 F.):

With respect to the'criticalphysical data, the

following may be observed:

Rubber-swelling 0.013 (heated 5 *days@ 158 F.)

Viscosity -.40F. -i 1902.6 0, s. Corrosion (6 days 200 F.)

Brass 0:4 mg./'sq.. cm.

Copper 0.0

Cast iron ..0.0

Steel 0:2

Aluminum-alloy 0.0

Tin 040' A still further specific example is represented by the following formulation:

Per cent by weight Tricresyl phosphate (.Tjech.) 18100 Dipropylene glycol 20.00 Ethyl ether of triethylene glycol 41.90 Ethyl ether of diethylene glycol M 20.00 Diisopropylamine nitrite 0.05 Diamylamine phosphate "0.05

The critical physical data for the foregoing formulation is as follows:

Rubber swelling(5 days 158 F.) 0.018" Corrosion (7 days (a) 158 FI) Ste'el .0.0 mg. sq. cm. Brass 0.2 Cast iron 023 Copper 0.1 Tin coated iron 0.1 Aluminum alloy 0.0

As stated, the principal advantage of the pressure transmission-fluids of .the present invention is that there is no' possibility of their oxidizing and forminga thick, tacky .film'on the moving parts of the hydraulic system. In testing the fluids for such tackiness, the following procedure was employed:

A complete wheel cylinder was assembled by lubricating the walls of the wheel cylinder, pistons, springs, and rubber cups with the fluid under test. 5100; of thelfluid wasadded to the cylinder with one port open. The cylinder was held at 70 C. for 14 days in a constant temperature oven. Examination of the cylinder and parts natthe -.endofthe"test shows no residue, gum or corrosion of any of the parts, indicating that there-was nooxidation of the ingredients.

.Aiurthen adyantage of the fluids of the pres- ;entzinvention resides in their miscibility with other commercial fluids in common usein brake systems'today. They also have good low tem- 'perature characteristics and are unusually inert astarvas rubber swelling is concerned. As a matter of fact, they do: not swell rubber at all. Intestconditionsthe diameter of arubber brake cup-isincreasedby such a. small .-amount .that it isdiificult to measurethe change with a micnometer. For. allpractical purposes it is zero: within experimental error.

The. fluids have good water tolerancehbeing;

miscible with water in all proportions. i Corrosion of the various. metalsin thehydraulics system can be held. under control by means of suitable.

inhibitors. Viscosities at.1-00..Ii?!."andv at -.40 F. establish a curve with a satisfactory slope.

What is. claimed is:

1. A hydraulic pressure fluid .consistingaessentially of the following. ingredients in the. approximate percentagesindicated:

Per. cent byweight Tricresyl phosphate 20.00 Dipropyiene glycol 14000 Ethyl ether-of. triethylene .g1ycol;. 239.10. Diamylamine phosphate 0305 Diisopropylamine nitrite 0105 2. A hydraulic pressure fluid consisting essen tially of the 'followingingredien'ts in the approximate percentages indicated:

.' Per cent by weight Trioresyl phosphate ..l 18.00 Dipropylene glycol ...I24.90 Hexylene glycol 15.00 Ethyl ether of triethylene glycol 42.00 Diisopropylamine nitrite 0.05 Diamylamine phosphate 0.05

.A. hydraulic pressure fluid consisting essentially of the following ingredients in the approximate percentages indicated:

Per cent by weight 'Ilricresyl phosphate 18.00 Dipropylene glycol 20.00 Ethyl ether oftriethylene glycol 41.90 Ethyl ether ofdiethylene glyco'l 20.00 Di-isopropylam-ine nitrite 0.05 Diamylamine phosphate 0.05

4. .A hydraulic. pressure .fluid -.consisting essential-ly of .at least 10% tricresyl phosphateas the sole lubricating base and the "remainder .at ieast onematerial. effective as a' diluent iorsaid tricresyl phosphate and selected from thengroup consisting of (1) can .alkyl ether ofua watersoluble glycol where the .alkylgroup contains 1-4 carbonatoms; (2) -a polyethylene glycol contain. ing .2-5 ethylene oxide groups; (3) apolypropylene glycol containing 2-3 propylene oxide groups; and (4) a water-soluble glycol whose alkylene group contains 4-6 carbon atoms.

5. A hydraulic pressure fluid consisting essentially of approximately 10-50% tricresyl phosphate as the sole lubricating base, approximately 50-90% of a material efiective'as a diluent for said tricresyl phosphate and selected from the group consisting of (1) an alkyl ether of a watersoluble glycol where the alkyl group contains 1-4 carbon atoms; (2) a polyethylene glycol containing 2-5 ethylene oxide groups; (3) a polypropylene glycol containing 2-3 propylene oxide groups; and (4) a water-soluble glycol whose alkylene group contains 4-6 carbon atoms, and approximately 0.1% of a corrosion inhibitor.

CHESTER M. WHITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

